An exemplary embodiment of this application relates to a variable pressure, belt driven sheet registration system for a sheet handling device. More particularly, the exemplary embodiment relates to a sheet edge registration system having a series of parallel driven belts. Each driven belt has a driven roller and an idler roller. The driven rollers are fixed to a common drive shaft and rotated thereby. The idler rollers each have an independent idler shaft about which the idler rollers may rotate, and the idler shafts are coaxially aligned and parallel to the common drive shaft of the driven rollers. Adjacent idler shafts are flexibly interconnected. A compression spring for each idler roller keeps the belts tensioned. The idler rollers and belts there around are cantilevered from the common drive shaft and may be pivoted there about. Thus, the gravitational force on the idler rollers and driven belts traveling around the idler rollers provide the necessary pressure or frictional acquiring force to register incoming sheets from a sheet transport. Selective pivoting of the idler rollers about the common drive shaft, in response to sheet media parameters that an end user inputs into the control panel of the sheet handling device, automatically varies the acquiring pressure applied by the belts on the incoming sheets to be registered.
Sheet handling devices may include document creating apparatus as well as finishing devices. In document creating apparatus, such as, for example, xerographic copiers and printers, it is increasingly important to be able to provide faster yet more accurate and reliable handling of a wide variety of image bearing sheets. Typically, the sheets are paper or plastic transparencies of various sizes, weights, and surfaces and may be subject to varying environmental conditions, such as humidity. Elimination of sheet misregistration at, for example, an imaging station of a copier or printer, is very important for proper imaging. In addition, sheet misregistration can adversely affect sheet feeding and ejection, as well as stacking and finishing of the sheets in a finishing device. While many document creating apparatus and finishing devices have adequate sheet registration systems, as delineated in the prior art listed below, none have an actively variable pressure sheet registration system that enables registration of a much broader range of acceptable sheet media having various weights, sizes, and coatings.
Sheet transporting devices are known to have driving nips that are typically designed to provide a normal force on the paper being transported therethrough that is sufficient to provide drive forces for sheets with particular media parameters without marking the sheet. However, as substrate or sheet mass increases, the potential for slip increases as well. Normal forces in the driving nip can be increased to offset this, but the potential for marking the lighter weight paper also increases. Thus, it is the aim of the exemplary embodiment of this application to provide automatic adjustment of the pressure or normal force of the driving nip of a registration system, in order to accommodate registration of a wide variety of sheet media.
U.S. Pat. Nos. 5,678,159 and 5,715,514 disclose dual differentially driven nips for automatic deskewing and side registration of sheets to be imaged in a printer, including the appropriate controls of the differentially driven sheet steering nips and including cooperative arrayed sheet edge position detector sensors and signal generators. As described therein, by driving two spaced apart steering nips with a speed differential to partially rotate a sheet for a brief period of time concurrently as the sheet is being driven forward by both nips, the sheet is briefly driven forward at an angle. Then the relative difference in the nip drive velocities is reversed to side shift the sheet into a desired lateral registration position as well as correcting any skew of the sheet as it entered the steering nips. Thus, the sheet exits the steering nips aligned in the process direction as well as being side registered.
U.S. Pat. No. 6,173,952 discloses a sheet handling system for correcting the skew and/or transverse position of sequential sheets moving in a process direction in a sheet transport path of a reproducing apparatus to be registered for image printing. The deskewing and/or side registration is accomplished by partially rotating the sheet with a transversely spaced pair of differentially driven sheet steering nips. The range of sheet size capabilities of this system may be increased without steering nip slippage or other problems by applying a control signal proportional to the width of the sheet to the system for automatically increasing or decreasing the transverse spacing between the pair of sheet steering nips. This is accomplished by automatically engaging only a selected pair of steering nips out of a plurality of different fixed position sheet steering nips and disengaging the others by lifting their idlers out of the sheet path with cams rotated by a stepper motor. The rotation of the cams by the stepper motor is controlled by the sheet width signal.